If you need to control visibility on the Task level, and you do NOT want those Users to be able to Assign Task Responsible, the User must have the following User settings:
User Role: Project Member
Process Group (Settings > Permissions): Member
Project Group: Edit
If you DO want those Users to be able to Assign Task Responsible, their workspace User Role should be Associate. But please note that when assigning Tasks, Associates will be able to see a list of ALL the Users in your workspace. See the article here for Task Permissions for Associates.
After adding the Users to the desired Project Group, open Tasks, and navigate to Root Level Permissions (top right). This will bring you to a page where you can set Permissions for a Group on the highest level of the Task list.
Permissions set at the highest level, will also be applied to the subtasks. So if you change the top level Task Permission to Edit, that Group will have Edit rights to all sub-Tasks in that section.
If you need to restrict access further, go back to the Task Tree, select the Task you want to change Permissions for, and click the Permissions icon (right side).
Please follow the guides below to understand what each Task Permission level allow a Project Member to do.
VDR Guests will have have the same Permission options, but because they have a different UI, each Permission level will mean something different. Please see the VDR Permissions article for more information.
A Parent Task will automatically change to Read Only if access to a subtask is given.
Note: Project Members with Project Group Edit access do NOT have access to Issues/Risks.